There are known optical pick-up devices for carrying out recording and/or reproduction of information with respect to optical disc, e.g., magneto-optical disc, etc.
The optical pick-up devices of this kind include an optical system including an object lens (objective) and an object lens drive unit for allowing object lens to undergo drive displacement in a direction in parallel to optical axis of object lens and in a direction perpendicular to the optical axis of the object lens.
The optical system includes a light source for emitting laser beams, the object lens for irradiating laser beams onto recording area of optical disc, a detector for receiving return light from the recording area of the optical disc, and various optical parts constituting the optical system.
The object lens drive unit includes, e.g., a lens holder for holding object lens, a holder supporting member for supporting this lens holder so that it is permitted to undergo displacement, plural elastic supporting members for permitting the lens holder to undergo elastic displacement, and an electromagnetic circuit section for allowing the lens holder to undergo drive displacement in a focusing direction in parallel to the optical axis of the object lens and in a tracking direction perpendicular to the optical axis of the object lens.
The lens holder is formed by, e.g., resin material, and includes a lens holding portion for holding the object lens. At the holder supporting member, a supporting portion for supporting the lens holder is formed, and an opening through which the optical axis of the object lens is passed is formed on the principal surface.
The elastic supporting member is formed by metallic material having elasticity so that it is linear. The elastic supporting member is adapted so that one end is fixed at the lens holder and the other end is fixed at supporting portion of the holder supporting member. Accordingly, the lens holder is supported at the holder supporting member through plural elastic supporting members so that it is permitted to undergo elastic displacement.
The electromagnetic circuit section includes a drive magnet and a drive coil which generate electromagnetic drive force, and a yoke constituting magnetic path. The drive coil includes a focusing coil and a tracking coil for respectively generating drive forces in the focusing direction and in the tracking direction.
In the above-described optical pick-up, the object lens held by the lens holder is moved in the focusing direction and in the tracking direction by the object lens drive unit. Thus, there are carried out recording and/or reproduction of information with respect to an arbitrary recording track of the optical disc.
The optical pick-up thus constituted is assembled with respect to base unit including feed mechanism for carrying out feed movement of the optical pick-up in the radial direction of the optical disc, disc rotation drive mechanism for rotationally driving the optical disc, and base chassis on which the feed mechanism and the disc rotation drive mechanism are provided. Thus, there is provided reproduction system of the optical disc.
The feed mechanism that the base unit has comprises a slide base for supporting the optical pick-up, a feed shaft for moving this slide base in the radial direction of the optical disc, a guide portion for movably supporting the slide base, and a drive mechanism for carrying out movement operation of the slide base. At the slide base, there are respectively formed a bearing portion movably supported by the feed shaft and a guide piece movably supported by the guide portion. The feed shaft is adapted so that the axial direction is caused to be in parallel to the radial direction of the optical disc and both ends are supported on the base chassis. In this feed mechanism, the slide base is moved in the radial direction of the optical disc along the feed shaft and the guide portion through the drive mechanism, whereby the optical pick-up is moved to an arbitrary recording track of the optical disc. Thus, information is reproduced from the optical disc.
The disc rotation drive mechanism includes a disc table on which optical disc is mounted and a spindle motor for rotationally driving this disc table. The disc table is attached on the rotation shaft of the spindle motor. The spindle motor is provided on the base chassis.
In the above-described optical pick-up, at the assembling step, in order to adjust relative position between the object lens and the light source and inclination of the optical axis of the object lens, there is used an adjustment apparatus for optical pick-up.
As an adjustment method for optical pick-up, two adjustment methods are used when roughly classified. The adjustment is carried out by the first adjustment method for carrying out adjustment by the optical pick-up itself and by the second adjustment method for carrying out adjustment in the state where the optical pick-up is assembled on the slide base of the base unit.
Initially, in the first adjustment method, optical pick-up to be adjusted is mounted on the slide base of the base unit where the feed mechanism and the disc rotation drive mechanism are provided with high accuracy as mechanism for adjustment. Thus, position and inclination of the optical axis of the object lens are adjusted.
At the base unit, the feed shaft of the feed mechanism is assembled with high accuracy on the base chassis as positioning reference of the optical pick-up, and the feed mechanism and the disc rotation drive mechanism are assembled with high accuracy with the feed shaft being as reference.
As shown in FIG. 1, a first adjustment apparatus (unit) 201 for carrying out adjustment of optical pick-up by the first adjustment method comprises a supporting mechanism 222 for adjustment including a slide base 220 for adjustment on which an optical pick-up 205 is mounted, a reference shaft 221 for movably supporting this adjustment slide base 220, and a supporting member 223 for supporting the slide base 220 with the reference shaft 221 being as reference.
Further, this first adjustment unit 201 comprises, as shown in FIG. 1, a lens adjustment mechanism 225 for adjusting position of an object lens 207 of the optical pick-up 205, a light source adjustment mechanism 226 for adjusting position of a light source 210 of the optical pick-up 205, an aberration detector 227 for measuring aberration in order to adjust positions of the light source 210 and the object lens 207 of the optical pick-up 205, a disc rotation drive mechanism 228 for rotationally driving an optical disc 211 for adjustment, and a disc movement mechanism 229 for moving this disc rotation drive mechanism 228.
At the adjustment supporting mechanism 222, as shown in FIG. 1, there is mounted the optical pick-up 205 on the slide base 220 for adjustment movably provided with the reference shaft 221 supported at a predetermined position by the supporting member 223 being as reference. The lens adjustment mechanism 225 includes a lens holding arm 231 for holding a lens holder 208 of the optical pick-up 205 to thereby hold the object lens 207, and movement mechanism (not shown) for moving this lens holding arm 231. The light source adjustment mechanism 226 includes a light source holding arm 234 for holding the light source 210, and movement mechanism (not shown) for moving this light source holding arm 234. As shown in FIG. 1, the aberration detector 227 is disposed at the position opposite to the object lens 207 of the optical pick-up 205, and is movably provided in a direction perpendicular to the optical axis of the object lens 207. The disc rotation drive mechanism 228 includes, as shown in FIG. 1, a disc holding member 237 for holding the adjustment optical disc 211, and a spindle motor 238 for rotationally driving this disc holding member 237. The disc movement mechanism 229 includes a guide member 239 for movably supporting the disc rotation drive mechanism 228, and movement mechanism (not shown) held by the disc rotation drive mechanism 228 and for moving the adjustment optical disc 211 in the radial direction of the adjustment optical disc 211 relative to the optical pick-up 205 along the guide member.
In accordance with the first adjustment unit 201 thus constituted, the adjustment optical disc 211 is rotationally driven by the disc rotation drive mechanism 228. As a result, the adjustment optical disc 211 is moved in the radial direction with respect to the object lens 207 by the disc movement mechanism 229. Further, position of the optical axis of the object lens 207 of the optical pick-up 205 is adjusted by the lens adjustment mechanism 225 and position of the light source 210 of the optical pick-up 205 is adjusted by the light source adjustment mechanism 226. In addition, adjustment is made such that there results a position where measured value that the aberration detector 227 measures is optimum.
In accordance with this first adjustment unit 201, the optical pick-up 205 is adjusted as single body so that the feed mechanism and the disc rotation drive mechanism are assembled with respect to base units respectively provided with high accuracy at ideal positions with respect to the feed shaft serving as the reference shaft, whereby they exhibit most performance.
Accordingly, in accordance with this first measurement method, the optical pick-up 205 can be adjusted as single body with high accuracy in the state where performance is guaranteed. Thus, it is possible to provide high accuracy optical pick-up 205 single body. In addition, since the optical pick-up thus adjusted can be assembled with respect to various base units different in specification such as configuration, etc., wide use characteristic is ensured.
However, in the first adjustment method, there exists inconvenience such that there exist unevenness in each assembling accuracy such as warp or inclination, etc. of the feed mechanism and the disc rotation drive mechanism or base chassis of base unit where optical pick-up 205 is assembled with respect to slide base 220 for adjustment in which the feed mechanism and the disc rotation drive mechanism have been caused to undergo positioning with high accuracy with respect to the reference shaft 221, whereby there takes place unevenness in assembling accuracy as the reproduction system followed by the above-mentioned unevenness.
As stated above, in the first adjustment method, in the case where the optical pick-up 205 is assembled with respect to base unit in which assembling accuracy is poor, performance as the reproduction system is lowered.
At the base unit, respective unevennesses of, e.g., the degree of plane of base chassis, inclination of rotation shaft of the spindle motor, plane vibration or eccentricity at the time of rotation of the disc table, and positional accuracy of the feed shaft, etc. are combined so that there takes place unevenness. For this reason, when actual productivity or production cost, etc. is taken into consideration, it cannot but tolerate that there takes place unevenness within a predetermined range.
In addition, in the optical pick-up 205 which has been adjusted, it is difficult to allow unevenness by adjustment to be zero, and there takes place unevenness of a predetermined distribution. For this reason, as the result of the fact that distribution of unevennesses of the adjusted optical pick-up 205 and distribution of unevennesses of base unit on which this optical pick-up 205 is assembled are combined, there is the possibility that there is constituted reproduction system in which unevenness greatly deviates from the allowed range.
On the other hand, as the second adjustment method, the single body of optical pick-up 205 is assembled with respect to the base unit, and position and inclination of the optical axis of the object lens 207 are adjusted as the entirety of the base unit. Thus, the optical pick-up 205 is assembled with high accuracy as the reproduction system.
As shown in FIG. 2, a second adjustment apparatus (unit) 202 for carrying out adjustment of the optical pick-up 205 by the second adjustment method comprises a lens adjustment mechanism 241 for holding a holder supporting member 209 of the optical pick-up 205 to adjust the object lens 207, a base holding mechanism 242 for holding a slide base 256 of base unit 206, a light source adjustment mechanism 243 for adjusting position of light source 210 of the optical system of the optical pick-up 205, and a detecting mechanism 244 for detecting optical characteristic of laser beams emitted from the object lens 207 which has been adjusted.
Moreover, at the base unit 206 held by the base holding mechanism 242, as shown in FIG. 2, there are provided, on a base chassis 251, a disc rotation drive mechanism 252 including a disc holding member 253 for holding optical disc 211 for adjustment and a spindle motor 254 for rotationally driving this disc holding member 253. Further, this base unit 206 includes the slide base 256 on which the optical pick-up 205 is assembled, a feed shaft 257 for movably supporting this slide base 256, and a feed motor 258 for allowing the slide base 256 to undergo feed operation.
The lens adjustment mechanism 241 includes, as shown in FIG. 2, a lens holding arm 261 for holding lens holder 208 of the optical pick-up 205 to thereby hold the object lens 207, and movement mechanism (not shown) for moving this lens holding arm 261. The base holding mechanism 242 includes, as shown in FIG. 2, a supporting member 264 for supporting the base unit 206, a base 265 on which this supporting member 264 is vertically provided, and an engagement member 266 engaged with the slide base 256 to carry out positioning. The light source adjustment mechanism 243 includes, as shown in FIG. 2, a light source holding arm 267 for holding the light source 210 of the optical pick-up 205, and movement mechanism (not shown) for moving this light source holding arm 267. The detection mechanism 244 includes a CCD (charge-Coupled Devices) camera 269 for detecting optical characteristic of laser beams emitted from the object lens 207.
In accordance with the second adjustment apparatus (unit) 202 thus constituted, optical disc 211 for adjustment is rotationally driven by the disc rotation drive mechanism 252 of the base unit 206. As a result, position of the optical axis of the object lens 207 of the optical pick-up 205 is adjusted by the lens adjustment mechanism 241, and position of the light source 210 of the optical pick-up 205 is adjusted by the light source adjustment mechanism 243. Thus, adjustment is made such that there results position where optical characteristic that the detection mechanism 244 detects is optimum.
In accordance with the second adjustment method, even if there respectively exist unevennesses in respective constituent parts of respective base units on which the optical pick-up 205 is assembled, adjustment is carried out in the state where the optical pick-up 205 is assembled with respect to the base unit 206, whereby unevenness as the assembled reproduction system can be reduced as compared to that of the reproduction system in which the optical pick-up 205 adjusted by the first adjustment method as described above is assembled with respect to the base unit.
Meanwhile, in the above-mentioned second measurement method, as shown in FIG. 3, in the state where the lens holder 208 which holds the object lens 207 or the holder supporting member 209 is held with high accuracy by the lens adjustment mechanism 241, and the slide base 256 is held with high accuracy at a predetermined position by the engagement member 266 of the base holding mechanism 242, the light source 210 or the optical system is held by the light source adjustment mechanism 243 so that adjustment is carried out. At this time, the slide base 256, the holder supporting member 209 and the light source 210 are respectively separately held, and adjustment is made by relatively moving these respective portions by very small quantity. For this reason, it is impossible to carry out feed operation in inner and outer circumferential directions of the optical disc 211 for adjustment. In order to carry out the feed operation in the above-described state, it is necessary to carry out movement so that relative positions are not changed in the state where the slide base 256, the holder supporting member 209 and the light source 210, etc. are respectively held. It is very difficult to realize such a movement.
However, when the second adjustment unit 202 reads information from recording track of the adjustment optical disc 211 in the state where the adjustment optical disc 211 is rotated at the time of adjustment, pit trains of the adjustment optical disc 211 are recorded in spiral form from the inner circumferential side toward the outer circumferential side. For this reason, the object lens 207 is gradually moved in the outer circumferential direction followed by rotation of the adjustment optical disc 211. In this adjustment unit 202, at the time of adjustment, the object lens 207 of the optical pick-up 205 is moved in the outer circumferential direction of the adjustment optical disc 211, whereby it is changed from the state of zero of visual field swing shown in FIG. 4A to the state of visual field swing which has been carried out shown in FIG. 4B. For this reason, the optical axis of the object lens 207 deviates (positionally shifts) with respect to the optical design center (hereinafter referred to as optical center) such as center, etc. of the light source 210. This adjustment method has the problem that since the optical axis of the object lens 207 deviates with respect to the optical center so that the optical characteristic is degrated and jitter value, etc. of detected reproduction signal is also degrated, it becomes very difficult to carry out adjustment in the case where, e.g., the optical axis of the object lens 207 is included to measure change of reproduction signal to allow the point to be measured to be in correspondence with the most favourable or best point to thereby adjust inclination of the optical axis of the object lens 207, etc.
As the countermeasure of this problem, various countermeasures are conceivable. In the case of carrying out adjustment of single body of the optical pick-up 205, the adjustment optical disc 211 is relatively moved in the inner circumferential direction and in the outer circumferential direction with respect to the slide base, the base chassis and the light source 210, etc. held by the base holding mechanism, whereby adjustment can be carried out while continuously reading information from the adjustment optical disc 211 in the state where the optical axis of the object lens 207 is not positionally shifted from the optical center.
However, even when this method is employed, in the case where consideration is rigorously made, as shown in FIG. 5, since lower frequency component of tracking error signal is extracted to carry out control of feed operation, it is impossible to carry out feed operation of the adjustment optical disc 211 if d.c. component of the tracking error signal is above a predetermined value.
Accordingly, with respect to the optical axis and the optical center of the object lens 207, there is carried out intermittent operation in which agreement or disagreement are repeated within a predetermined range. In this connection, pitch of this intermittent operation is about several 10 μm from a practical point of view.
Moreover, as another method, there is a method in which when the optical axis of the object lens 207 produces a predetermined positional shift with respect to the optical center, application of tracking servo is released to carry out feed operation toward the inner circumferential side of the adjustment optical disc 211 by positional shift quantity (hereinafter referred to as track jump) to thereby allow the optical axis of the object lens 207 to fall within the range of a predetermined positional shift quantity at all times with respect to the optical center.
However, if the number of rotations of the adjustment optical disc 211 is caused to be, e.g., 5 rotations/sec. (5 Hz) and the track pitch of recording tracks of the adjustment optical disc 211 is 1.6 μm, the optical axis of the object lens 207 is moved with respect to the optical center by 8 μm per one second, 40 μper five seconds ≈25 tracks. In practice, the optical axis of the object lens 207 is moved from the position of 40 μm at the inner circumferential side of the adjustment optical disc 211 with respect to the optical center, and the optical center and the optical axis of the object lens 207 are caused to coincide with each other after five minutes have been passed. At the time point when the optical axis of the object lens 207 is moved by 40 μm with respect to the optical center after five minutes have been further passed, application of tracking servo is released to carry out track jump by 80 μm≈50 tracks moved toward the inner circumferential side.
As stated above, the tracking servo and the track jump are carried out, thereby making it possible to adjust the optical axis of the object lens 207 so that it falls within the range of ±40 μm. However, in this method, even when the optical axis of the object lens 207 is caused to fall within the range of ±40 μm, the optical axis and the optical center of the object lens 207 are moved at all times. For this reason, there is the inconvenience that it is difficult to detect true value at the time of adjustment. Further, in this method, because time when tracking servo is stably applied is short, it takes much time in order that stable true value is measured by measurement instrument, e.g., jitter detector,etc. after track jump. For this reason, there is an inconvenience such that adjustment is difficult because time when position, etc. of optical axis of the object lens 207 can be adjusted is very short in practice. Further, in this method, there is the problem that when the interval of track jump is widened, positional shift of the optical axis of the object lens 207 is further increased.
In addition, in the case of a method of carrying out adjustment in the state where optical pick-up 205 is assembled on the base unit as shown in FIG. 6, it is impossible to move optical disc 211 for adjustment with respect to the base for adjustment. For this reason, when methods except for the method of repeating track jump are employed, adjustment is difficult. However, since there exist the above-described problems in this method, it is impossible to precisely carry out adjustment.